1. Field of the Invention
The present invention relates to an image forming device that includes a heat fixing mechanism, such as a copying machine, a facsimile machine, a printer, or the like. More specifically, the present invention relates to an image forming device that is capable of detecting a paper jam in the heat fixing mechanism.
2. Description of the Related Art
In an electrophotographic-type image forming device, output image data is generated by applying prescribed image processing on manuscript image data that is read by an image reading part, light beams modulated based on the output image data are irradiated on a surface of a photoreceptor that is charged uniformly, an electrostatic latent image formed on the photoreceptor is developed with toners, a toner image obtained thereby is transferred from the photoreceptor to a paper, the toner image on the paper is then thermally fixed at a fixing part, and the paper is discharged.
The fixing part is constituted with: a fixing roller that includes a heater inside thereof and a pressure roller that is disposed in a coaxial direction with respect to the fixing roller to press a paper against the fixing roller. A paper to which a toner image is transferred is sandwiched between the fixing roller and the pressure roller, and transported from an upstream side of a transporting path of the paper towards a downstream side thereof while being heated under a pressure. That is, the fixing part has a function of thermally fixing the toner image to the paper as well as a function of transporting the paper. Further, there is also a fixing part including a fixing belt in a belt-like form that is different from the fixing roller. However, the functions thereof are the same as the functions of the fixing roller described above.
In general, the image forming device is provided with a paper detecting part for detecting a paper that passes through the fixing part, and a paper jam detecting part for detecting an occurrence of a paper jam based on a detection state of the paper detected by the paper detecting part. This makes it possible to detect occurrences of abnormal states, e.g. a state where a paper is wrapped around the fixing roller or the pressure roller, and a state where a paper is stuck within the fixing part.
When the paper jam detecting part detects a paper jam, the heater of the fixing roller is turned off and the image forming device is stopped at the same time. It is then controlled to wait until the paper within the fixing part is removed.
Further, if the image forming device is returned to a normal state without removing the paper stuck in the fixing part, a paper transported thereafter is also stuck in the fixing part, which gives critical damages to the fixing part, or deteriorates the paper-jam state so that it becomes difficult to remove the papers. Therefore, when the image forming device is returned to the normal state after the occurrence of the paper jam in the fixing part, a paper detecting sensor detects whether or not there is a remaining paper.
However, the paper detecting part is disposed away from the fixing roller in order to avoid an influence of a high temperature from the fixing part. Thus, when a paper jam is detected at the paper jam detecting part, there is a high possibility for a rear end of a long paper to be detected by the paper detecting part, while there is a low possibility for a short paper to be detected because a rear end of the short paper may already have passed the paper detecting part at a point where the paper jam is detected. In such cases, it is also difficult for an operator to visually check the paper. Therefore, the image forming device is returned to the normal state without having the paper removed, which may result in causing the above-described problems.
Japanese Unexamined Patent Publication No. 2002-189398 discloses an image forming device which includes: a fixation roller for fixing a toner image that is formed on a transfer paper to the transfer paper by heating and pressurizing it with a fixing roller and a pressure roller; roller driving means capable of changing a drive speed for rotationally driving the fixation roller forwardly and backwardly; and downstream-side jam detecting means for detecting a paper jam in a paper transporting path on a downstream side with respect to the fixation roller, wherein, when a jam of a paper tip is detected by the downstream-side jam detecting means, a drive of the fixation roller is stopped after it is driven at a lower speed than a speed at the time of forming an image and driven in an opposite direction with respect to a direction at the time of forming the image.
However, as in the image forming device depicted in Japanese Unexamined Patent Publication No. 2002-189398, to drive the fixation roller in a reverse direction indiscriminately upon detecting a paper jam is not a solution to sufficiently overcome such problems, i.e. the fixation roller is damaged depending on the paper jam state, and the paper jam state is deteriorated so that it becomes difficult to remove the paper.